Fuel injection systems have replaced carburetors in most modern aircraft engines. Presently, fuel injection systems provide greater performance, economy, and reliability relative to their carburetor counterparts.
Most prior art fuel injection systems used in aircraft engines are volume-air flow type systems, which are based on the principle of measuring air flow to establish correct fuel flow to the engine cylinders. These systems include a throttle body fuel injection servo which measures the amount of air moving past the throttle by use of a venturi. An in-line diaphragm type flow regulator then converts the air pressure from the venturi into a proportional fuel pressure. During normal operation of the aircraft engine, the position of the throttle controls the air flow through the fuel injection servo or to the regulator, which then controls the flow of fuel to the cylinders. The servo is the primary component used in the fuel injection system and performs all functions required to establish fuel flow volumes. The regulated fuel flow from the servo is sent to a fuel flow divider, which divides the steady stream of fuel into smaller streams of fuel, one for each cylinder. Fuel lines carry fuel from the divider to injector nozzles located in the intake ports of each cylinder. The injectors supply fuel to the intake manifold. Fuel then enters the cylinders from the intake manifold under the low pressure created in the cylinder during the intake cycle.
During normal operation of the aircraft engine, the position of the throttle and the air flowing through the fuel injection servo or flow regulator controls the flow of fuel to the cylinders of the aircraft engine. As the throttle is opened, more fuel is delivered to each cylinder, resulting in an increase in the speed of the engine or in manifold pressure, and thus more power being generated by the engine. Generally, most fuel injection servos include an air passage mechanism (i.e., the throttle body), a fuel pressure modifying mechanism (i.e., the valve assembly), and a fuel regulator assembly.
FIG. 1 is a schematic cross-sectional view of a prior art fuel injection system as representative of a Precision Airmotive, LLC brand RSA-5AD1™ RSA-5AB1™ or RSA-10AD1™ system. In the top-left of FIG. 1, a valve assembly 100 is shown that includes a mixture control valve 101 and idle control valve 102. The fuel injection system includes a fuel inlet to accept fuel from, for example, a fuel pump (not shown) before directing such fuel through the fuel strainer and into the cavity housing the mixture control valve and idle control valve. The mixture control valve 101 is connected to the manual mixture control lever 10. A throttle valve is connected to the idle valve lever 12. Within the valve assembly cavity housing is also a metering jet for the delivery of fuel, whereby the idle control valve 102 regulates the metered fuel pressure (shown in dark pink) and the mixture control valve regulates the unmetered (inlet) fuel pressure (shown in red), each to separate sides of a fuel diaphragm housed within the fuel regulator of the servo system.
The valve assembly (i.e., fuel pressure modifying mechanism) receives fuel from a fuel supply and delivers the fuel at a pressure that is different from the fuel supply to the fuel regulator assembly. Some of the major components of valve assembly include an idle valve assembly and a mixture valve assembly. The mixture valve assembly as shown in FIGS. 1 and 2 includes a mixture valve connected to the mixture control lever 10. The mixture valve often has a hollow barrel design of cylindrical shape that allows for rotational operation within a bore formed in the valve body. At one end of the mixture control assembly shaft is a roll pin 12 engaged with the shaft 14 adjacent a clip. About the shaft is a spacer 18, clip 16 and thrust disc 20, where the flat surfaces are pressed against one by way of a spring 11 that presses against a spring seat 13. The spring 11 wraps around the exterior of the shaft and variably a portion of the bushing 15. The bushing 15 may engage the shaft though various seals 17. The lever 10 is connected to the end of the shaft opposite the clip 16, spacer 18 and thrust disc 20, at a point relative to where a second roll pin 12a is positioned. Hole(s) in the non-rotation disc through which fuel can flow, and the hole(s) in the mixture valve shaft can align, permitting the flow of fuel. When misaligned, the fuel is shut off. The discs and hole(s) can also partially permit flow when in intermediate positions.
The traditional mixture control assembly is shown in FIGS. 4A-4D, where measurements are relative and may not be drawn to scale. The spring 11 can be seen imparting pressure on the spring seat 13, and thereon to the thrust disc 20 and clip 16 and/or spacer 18 encircling the shaft. In this example, the spring is noted as 0.854 inches in length down the shaft. The mixture control assembly may also include a stop bracket 75.
The idle valve assembly shown in FIGS. 3A and 3B include an idle valve that is connected to the throttle linkage via an idle valve lever 38. The idle valve often has a hollow barrel design of cylindrical shape that allows for rotational operation within a bore formed in the valve body. The idle valve generally includes an opening 31 (e.g., a notch cut approximately half way into the side of valve) which communicates with a channel 32 of the regulator assembly for delivering metered fuel to the regulator. At one end of the opening is often a stepped slot 31. The idle valve effectively reduces the area of the main metering jet for accurate metering of the fuel in the engine idle range.
The idle valve assembly shown in FIGS. 1 and 3 generally includes an idle valve cover (not shown), a thrust washer/disc 35 (generally, polymer or Teflon), an idle lever spacer, and an o-ring seal. The idle valve shaft may further include a flat disc-like flange 30 having small holes or slots 31 therein. The flat disc-like flange 30 (polymer or Teflon) may be held against a second non-rotating flat disc 33 (polymer or Teflon) by a spring (shown in FIGS. 1 and 2) in such a way that the two flat surfaces of the discs are pressed against one another. In certain other embodiments, the second non-rotating flat disc 33 may be positioned opposite and spaced apart from the disc-like flange 30, wherein the flat disc 33 pushes against a polymer washer 35 to reduce friction. In either configuration, the hole(s) in the non-rotation disc through which fuel can flow, and the hole(s) in the idle valve shaft can align, permitting the flow of fuel. When misaligned, the fuel is shut off. The discs and hole(s) can also partially permit flow when in intermediate positions.
The spring load imposed on the discs creates a load on the shaft tending to push in a direction towards outside of the servo housing. Various efforts have been made to alleviate the friction associated with the discs and other components. For example, polymer thrust washers have been employed for years and are sufficiently durable, but do not reduce friction as is desired. Teflon washers are also utilized, but friction remains.
The friction and stiffness resulting from the spring-load bearing washer system (“thrust washers”) results in throttle friction. Such stiffness has also led to ‘jumpy’ control settings. Worse, microscopic wear particles thought to be generated from the thrust washers may coalesce with certain constituents (or contamination) in the aviation gasoline found in various regions around the world, particularly the south Asia region. These particles are purported to form particle aggregations that flow downstream, contaminating the fuel system.
The spring tension and size, coupled with the clip(s) (e.g., c-clip), washers, and other components leave little room for modifications, particularly where such componentry has long been approved by the Federal Aviation Administration.
A fuel injection system which avoids the shortcomings attendant with the prior art devices and practices utilized heretofore is the subject matter of the present application. The throttle control lever is mechanically linked to a valve which controls fuel to the engine when the throttle is at or very near closed (idle). In various fuel injection servo systems, when the throttle is moved, the idle valve moves. It is often in the idle valve assembly that the high friction affecting throttle movement occurs.